There is conventionally known a technique for controlling a continuously variable transmission of the type having a variator and a clutch arranged in series with the variator, wherein the clutch is set to a neutral position upon recovery (power reset) from the occurrence of an instantaneous interruption in a control system during running. By this control, a change in operating state due to the power reset is suppressed from being transmitted to drive wheels (see, for example, Patent Document 1).
However, the above conventional technique still has the following problem even though it is possible by the conventional technique to suppress a change in vehicle behavior before and after the occurrence of the instantaneous interruption in the control system.
When power is reset during running, the vehicle speed sensor value is set to zero on the assumption that an ignition switch is turned on during parking. Then, both of the desired transmission ratio and the target transmission ratio of the variator are set to a lowest transmission ratio value by initialization processing. At this time, the actual transmission ratio of the variator is not equal to the lowest transmission ratio value and is in the vicinity of a transmission ratio value at the occurrence of the instantaneous interruption. The desired transmission ratio is thus changed, immediately after the power reset, to the vicinity of the transmission ratio value at the occurrence of the instantaneous interruption. On the other hand, the target transmission ratio is set to the lowest transmission ratio value. Consequently, the variator starts to downshift from the vicinity of the transmission ratio value at the occurrence of the instantaneous interruption to the lowest transmission ratio value so as to adjust the actual transmission ratio to the target transmission ratio.
It however takes a long time to converge the target transmission ratio to the desired transmission ratio, which is determined according to vehicle running conditions, in the case where the target transmission ratio is changed from the lowest transmission ratio value to the desired transmission ratio at the same speed as under normal control. Namely, the time during which the target transmission ratio is lower than the desired transmission ratio is long. This results in a problem that the rotation speed of the engine may become unnecessarily high due to a long duration of the downshift in which in which the input rotation speed of the transmission is set high.